A problem associated with smoking articles such as cigarettes or cigars is the amount of sidestream smoke that is given off during static burning, for example when the smoking article is idling and not being drawn upon by the smoker or is simply resting in an ashtray while burning. Visible sidestream smoke that is given off by a smoking article such as a cigarette during static burning is irritating and objectionable to nonsmokers in the vicinity of the idling cigarette.
A problem with heretofor developed wrappers that produced low sidestream smoke is that they give a flaky and/or off color ash due to poor ashing characteristics of the wrappers. Various mechanisms have been incorporated into smoking articles to reduce visible sidestream smoke and to improve the ashing characteristics of wrappers, but none to date has been commercially successful in overcoming both of these problems.
Probably the most effective means of reducing visible sidestream smoke, to date is disclosed and claimed in U.S. Pat. No. 3,231,377, Cline et al owned by applicant's assignee. Olin Corporation.
In this patent there is disclosed a wrapper for smoking articles such as cigarettes, cigars and the like containing at least 15% by weight magnesium oxide or its hydrate and at least 0.5% by weight of specific chemical adjuvant such as the alkali metal acetates, carbonates, citrates, nitrates or tartrates. The combination of magnesium oxide or its hydrate with any of the chemical adjuvants significantly reduces visible sidestream smoke that emanates during static burning from smoking articles employing the wrapper. The wrapper may comprise conventional cigarette paper with magnesium oxide and the adjuvant incorporated therein as the filler in the paper furnish or either or both of the additives may be applied to the paper as a coating. Wrappers containing the additives can be used in place of conventional wrappers for smoking articles or used as an inner wrapper for the tobacco column in combination with a conventional outer wrapping of cigarette paper or cigar wrap.
Following the teaching of this patent substantial and very desirable reduction in visible sidestream smoke can be achieved by using cigarette paper containing magnesium oxide as a filler in combination with certain chemical adjuvants. These papers have consistently given a flaky ash and have been determined to be unacceptable for use by the cigarette manufacturers due to the poor ashing characteristics. Extensive testing has not identified any chemical adjuvant or burning chemical or combination thereof which overcomes this problem.
The more reactive grades of magnesium oxide which are very effective as sidestream reducing fillers are at least partially converted to magnesium hydroxide during the papermaking process. MagChem 40, manufactured by the Martin Marietta Company, is an example of this type of product which gives a very flaky cigarette paper ash. In contrast, a hard-burned, unreactive magnesium oxide such as MagChem 10, produced by the same company, gives a white, solid ash which shrinks and holds on well. This unreactive oxide hydrates to give magnesium hydroxide only very slowly at ambient temperatures and remains essentially unchanged in the finished paper when used as a filler. Papers filled with unreactive magnesium oxide give no sidestream smoke reduction beyond that which can be achieved with calcium carbonate at equivalent high levels of basis weight, and burn rate accelerators.
These facts lead to the conclusion that magnesium hydroxide is a necessary ingredient if optimum sidestream reduction is to be achieved. It was speculated that if the effect of magnesium hydroxide on cigarette combustion was due to its endothermic dehydration at approximately 350.degree. C., then the yield of sidestream tar should be inversely related to the amount of magnesium hydroxide in the paper. This has been determined not to be entirely true. Thus, MagChem 40, completely hydrated by slurrying in water overnight, is no more effective than when used without pretreatment to make handsheets. Approximately 50% of the unpretreated filler was converted to magnesium hydroxide during the process of making the handsheets. Also, powdered magnesium hydroxide used as the only filler component gave no greater sidestream reduction than the partially hydrated oxide and gave a darker, very flaky ash.